1. Field of the Invention
The present invention generally relates to a transmission parameter recognition apparatus, and more particular, to a transmission parameter recognition apparatus for recognizing the guard interval type and the transmission mode.
2. Description of Related Art
In the digital communication field, every symbol transmitted by an orthogonal frequency division multiplexing system (OFDM system) includes a data interval and a guard interval. A transmission terminal can transmit data intervals in different lengths according to different transmission modes, and each transmission mode can select a guard interval with an appropriate length to avoid an inter-symbol interference (ISI) caused by the so-called multi-path effect (MPE) according to the practical need. Usually, the OFDM system applied in a digital video broadcasting-terrestrial system (DVB-T system) includes two kinds of transmission modes, “2K” mode and “8K” mode, wherein the guard interval lengths in each transmission mode include different fractions of a data interval length, namely ¼, ⅛, 1/16 or 1/32 data interval length.
Due to an OFDM signal in various transmission modes, the reception terminal must first detect the transmission mode and the guard interval type of the received symbols, so as to extract the correct data intervals. FIG. 1 is a diagram of a conventional correlation function processing module, employed by a conventional OFDM system for detecting the transmission mode and the guard interval type. As shown by FIG. 1, r[n] herein represents a sample sequence of an OFDM signal after analog-to-digital converting (ADC), which includes a plurality of symbols, for example, symbols 110, 120 and 130, and each of the symbols comprises a guard interval in a length of Ng (namely, Ng sample points) and a data interval in a length of Nu (namely, Nu sample points).
Since every symbol contains a repeating structure therein (for example, the guard interval 111 is a replica of the end portion 112 of the symbol 110), thus, the conventional function processor generates a conjugate product sequence according to the relation between two adjacent symbols and accumulates these values corresponding to all the sample points in the conjugate product sequence over the summing length Ng to generate a correlation function sequence, which includes a plurality of triangle-like waveforms, for example, 141 and 151, and the relation between the triangle-like waveforms implies the transmission mode information and guard interval type information.
The OFDM signal used in a DVB-T system includes two transmission modes (Nu=2048 and Nu=8192) and four guard interval types ((¼)Nu, (⅛)Nu, ( 1/16)Nu and ( 1/32)Nu). To extract the correct information, a conventional transmission parameter recognition apparatus, as shown in FIG. 2A, an architecture diagram of a conventional transmission parameter recognition apparatus, employs a set comprising four conventional correlation function processors 211-214 and a set comprising four conventional correlation symbol adders 221-224 to detect the implied transmission mode and guard interval type, wherein the summing length of the conventional correlation function processors 211-214 is respectively ( 1/32)Nu, ( 1/16)Nu, (⅛)Nu and (¼)Nu; while the conventional correlation symbol adders 221-224 respectively provide (Nu+( 1/32)Nu) sample memory points, (Nu+( 1/16)Nu) sample memory points, (Nu+(⅛)Nu) sample memory points and (Nu+(¼)Nu) sample memory points.
Continuing to FIG. 2B, when the guard interval length of a sample sequence r[n] is respectively ( 1/32)Nu, ( 1/16)Nu, (⅛)Nu and (¼)Nu, the sample sequence r[n] would respectively pass through the conventional correlation function processors 211-214 to output correlation function sequences C21[n]-C24[n], as shown by FIG. 2B. Then, the correlation function sequences C21[n]-C24[n] are respectively fed into the conventional correlation symbol adders 221-224 with different sample memory points for superposing the triangle-like waveforms in the correlation function sequences. After the superposing, the peaks of the triangle-like waveforms are more distinct, so that the guard interval and transmission mode recognition unit 230 is able to detect the plurality of peaks produced by the conventional correlation symbol adders 221-224 and to obtain the transmission mode and the guard interval type of the OFDM signal.
In order to simplify the hardware architecture of the conventional transmission parameter recognition apparatus 200, another conventional transmission parameter recognition apparatus as shown by FIG. 3A is provided. Referring to FIG. 3A, a conventional transmission parameter recognition apparatus 300 employs a conventional correlation function processor 311 and four conventional correlation symbol adders 321-324 to detect the transmission mode and the guard interval type, wherein the summing length of the conventional correlation function processor 311 is ( 1/32)Nu, while the conventional correlation symbol adders 321-324 respectively provide (Nu+( 1/32)Nu) sample memory points, (Nu+( 1/16)Nu) sample memory points, (Nu+(⅛)Nu) sample memory points and (Nu+(¼)Nu) sample memory points.
Continuing to FIG. 3B, when the guard interval length of a sample sequence r[n] is respectively ( 1/32)Nu,( 1/16)Nu,(⅛)Nu and (¼)Nu, after the sample sequence r[n] passes through the conventional correlation function processor 311, different correlation function sequences C31[n] are generated, wherein each of the correlation function sequences C31[n] respectively has a plurality of different triangle-like waveforms (for example, 341 and 342) or different trapezoid-like waveforms (for example, 351-356) in response to the different guard interval lengths. The transmission mode and guard interval information can be recognized from the triangle-like waveforms or trapezoid-like waveforms.
Therefore, the correlation function sequence C31[n] is passed through the conventional correlation symbol adders 321-324 with different sample memory points to superpose the triangle-like waveforms or the trapezoid-like waveforms thereof, so that a guard interval and transmission mode recognition unit 330 is able to obtain the transmission mode information and the guard interval information of the OFDM signal by judging the repeated periods of the triangle-like waveforms or the trapezoid-like waveforms or by judging the amount of energy contained in the triangle-like waveforms or the trapezoid-like waveforms possess.
The US patent published application No. 20020186791, for example, discloses a recognition apparatus having a hardware architecture similar to the above-mentioned conventional transmission parameter recognition apparatus 300, wherein the transmission mode information and the guard interval information of an OFDM signal are obtained by judging the periodic property of the occurred triangle-like waveforms or the trapezoid-like waveforms. The US patent published applications No. 20030219804, No. 20040223449 and No. 20040240379 also adopt a hardware architecture similar to the conventional transmission parameter recognition apparatus 300, wherein the transmission mode information and the guard interval information of the OFDM signal are obtained by judging the amount of energy contained in the triangle-like waveforms or the trapezoid-like waveforms.
Although the conventional transmission parameter recognition apparatus 300 tries to lower the quantity of the employed conventional correlation function processors for simplifying the adopted hardware architecture, however, the conventional transmission parameter recognition apparatus 300 still requires a plurality of conventional correlation symbol adders in coordination with the multiple guard interval types. In other words, the conventional transmission parameter recognition apparatus 300, limited by using a plurality of conventional correlation symbol adders, can not effectively reduce the hardware architecture complexity and lower the power consumption in practice.